The investigator describes several lines of evidence in favor of the hypothesis that retinal glia when subjected to hypoxic injury release VEGF and TGF-beta and promote the breakdown of the blood retinal barrier in slightly different ways. The applicant presents the hypothesis that TGF-beta stimulates VEGF release and VEGF has an NO-mediated effect to increase transcytotic permeability. TGF-beta, in contrast, is proposed to increase paracellular permeability by matrix metalloproteinase (MMP)-mediated breakdown of the intercellular extracellular matrix (ECM). The first aim of the study is to test the hypothesis that VEGF stimulates increased endothelial cell permeability by promoting transcytotic transport mediated by caveolae and nitric oxide (NO) signaling mechanisms. The second aim will test the hypothesis that TGF-beta stimulates increased endothelial cell permeability by mechanisms involving either the MMP gelatinase or VEGF. The third aim will test the idea that hypoxia induces endothelial cell hyperpermeability by promoting glial release of TGF-beta or VEGF. These studies will largely be carried out with cultured bovine endothelial cells. Since permeability increases promote tissue damage in various retinal diseases (e.g., ischemia, retinopathy of prematurity), it is important to understand the process leading to such increases so as to develop means for controlling it.